1. Field of the Invention
The invention relates to a system and device, more particularly, a power-over-Ethernet (PoE) relay system, a power injector and an access bridge device.
2. Description of the Related Art
Under the current infrastructure for Ethernet cabling layout, Power over Ethernet (PoE) is a technology using a networking cable for simultaneously supplying a direct current (DC) power (36V˜57V) to a terminal equipment in compliance with PoE specification, such as an IP phone, a wireless access point, a web camera, etc., while supplying network data thereto. It is relatively convenient this way that the terminal equipment can operate properly once it is coupled to a networking cable without the need for additional external power plugs or batteries to supply the power necessary for operation. PoE is also known as Power Over LAN (POL) or Active Ethernet that is compatible with the currently-existing Ethernet system and its clients. The IEEE 802.3at standard is the newest standard of the PoE system that adds a direct-powering-via-a-networking-cable standard to the IEEE 802.3af standard. It is the expansion of the current-existing Ethernet standard and the first international standard with respect to power distribution.
Referring to FIGS. 1 and 2 and according to the IEEE 802.3af standard, a complete PoE system includes: a PoE powering apparatus 21, a PoE powered apparatus 22 and a networking cable 23.
The PoE powering apparatus 21 includes a power sourcing equipment (PSE), two transformers 31, 32, and a connection port (such as a RJ45 connection port) having first to eighth pins 1˜8.
The PoE powered apparatus 22 includes a powered device (PD), two transformers 33, 34, and a connection port (such as a RJ45 connection port) having first to eighth pins 1˜8.
The networking cable includes four twisted pair cables 35, 36, 37, 38.
The twisted pair cable 35 is electrically coupled between the first and second pins 1, 2 of the PoE powering apparatus 21 and the first and second pins 1, 2 of the PoE powered apparatus 22.
The twisted pair cable 36 is electrically coupled between the fourth and fifth pins 4, 5 of the PoE powering apparatus 21 and the fourth and fifth pins 4, 5 of the PoE powered apparatus 22.
The twisted pair cable 37 is electrically coupled between the seventh and eighth pins 7, 8 of the PoE powering apparatus 21 and the seventh and eighth pins 7, 8 of the PoE powered apparatus 22.
The twisted pair cable 38 is electrically coupled between the third and sixth pins 3, 6 of the PoE powering apparatus 21 and the third and sixth pins 3, 6 of the PoE powered apparatus 22.
Powering in the PoE can be supplied in two ways, one of which is called end-span (as shown in FIGS. 1 and 2), where a DC power is transmitted to the PoE powered apparatus 22 simultaneously with the data signals (explained later), and the other one of which is called mid-span (as shown in FIG. 3), where the DC power is transmitted via the PoE powering apparatus 21 having a mid-span PSE. As the cabling connections of mid-span are similar to those of end-span and can be referred to in the IEEE802.3af standard, it is not described herein.
The end-span can be categorized into two types. The first type powers via the first and second pins 1, 2, and the third and sixth pins 3, 6 of the PoE powering apparatus 21 (as shown in FIG. 2), and the second type powers via the fourth and fifth pins 4, 5, and the seventh and eighth pins 7, 8 of the PoE powering apparatus 21 (as shown in FIG. 1).
As shown in FIG. 1, when the PoE powering apparatus 21 powers via the fourth and fifth pins 4, 5, and the seventh and eighth pins 7, 8, the fourth and fifth pins 4, 5 of the PoE powering apparatus 21 are electrically coupled to a positive terminal of the power sourcing equipment (PSE), while the seventh and eighth pins 7, 8 of the PoE powering apparatus 21 are electrically coupled to a negative terminal of the power sourcing equipment (PSE). The fourth and fifth pins 4, 5 of the PoE powered apparatus 22 are electrically coupled to a positive terminal of the powered device (PD), while the seventh and eighth pins 7, 8 of the PoE powered apparatus 22 are electrically coupled to a negative terminal of the powered device (PD).
As shown in FIG. 2, when the PoE powering apparatus 21 powers using the first and second pins 1, 2 and the third and sixth pins 3, 6, the power sourcing equipment (PSE) powers centers of the transformers 31, 32 by center tapping, while the powered device (PD) is electrically coupled to centers of the transformers 33, 34 also by center tapping without affecting network data transmissions. The first and second pins 1, 2 and the third and fourth pins 3, 6 can be of any polarity.
According to the IEEE 802.3af standard, the PoE powering apparatus 21 can only power through one of the two conditions of FIGS. 1 and 2, while the PoE powered apparatus 22 needs to be able to adapt to both conditions. Such requirement is easily achieved by PoE powered apparatus of 10 Mbps and 100 Mbps as only the first and second pins 1, 2 and the third and sixth pins 3, 6 are used to receive network data.
However, with the advancement of network technology, the PoE cabling infrastructure can now support transmission speeds of 1000 Mbps. At 1000 Mbps, the full use of the twisted pair cables is required for network data transmission, and the PoE relay systems defined in FIGS. 1 to 3 cannot meet all three requirements for 10 Mbps, 100 Mbps and 1000 Mbps simultaneously, thus restricting the development of PoE systems.
With a conventional embodiment of a one-to-many application for a PoE system, there arises a problem of high cost. For example, FIG. 4 shows a network power source unit (S1) having a PoE powering apparatus 21 coupled to two electronic products (P1, P2) that are disposed in a same area respectively via two lengthy networking cables 23. Each of the two electronic products (P1, P2) has a PoE powered apparatus 22. The network power source unit (S1) transmits network data and network power to the two electronic products (P1, P2) via the two networking cables 23. However, the need to use two lengthy networking cables 23 increases the cost.
For another example, FIG. 5 shows another conventional method to implement a one-to-many application in a PoE system with the difference of: the addition of a PoE access bridge device (AP1). The PoE access bridge device (AP1) has a PoE powered apparatus 22 electrically coupled to the PoE powering apparatus 21 of the network power source unit (S1) via a networking cable 23 to receive the network data and the network power, and a PoE powering apparatus 21 coupled to the two electronic products (P1, P2) respectively via two short networking cables 24. The PoE access bridge device (AP1) divides the network data. The PoE powering apparatus 21 of the PoE access bridge device (AP1) generates power to be carried with the divided network data to the two electronic products (P1, P2). Although the cost of providing lengthy networking cables 23 is saved, the use of costly PoE powering and powered apparatuses 21, 22 in the PoE access bridge device (AP1) increases cost. Also, the network power of 36V to 57V needs to be down converted to the range of between 5V and 12V so as power the PoE access bridge device (AP1), therefore the PoE access bridge device (AP1) will need an extra step-down converter (not shown in figure) that will further increase the hardware cost.